To the OP.
Don't discount the co-workers. Most of my friends are old enough to be my parents(although I am a bit of an "old soul"). Also, as previously stated, they may know people you might enjoy meeting. Older people have been great friends to me ever since I was a teenager. Some of the most influential and lasting friendships I have had have been with senior citizens.
There are tons of lonely people in every city in this country, and some of them will have common interests with you. One of the best ways I have found to make friends in a new area is simply to be friendly and helpful to people you meet. If there is a chance for conversation, capitalize on it. I moved to one of the most clannish areas of the Ozarks 8 years ago, and within two years my girls were "complaining" that they couldn't get away with anything because I knew everybody. Seriously, every time I go to town, I am running into someone I know. My oldest started the texting and driving thing when she got her license, it took less than a week for one of the cops in town to catch me at the cafe and tell me about it. Promptly broke her of the habit when she came home and I told her I knew, how I found out, and that the next time would see me yanking her car and license for a month. Admittedly, I started a business as soon as I moved here, and was politically active in the area for a while, both of which allowed me to meet a lot of people.
But there are myriad ways to meet people and turn them into friends. As the Good Book says, If a man will have friends, he must show himself to be friendly. The Chicago area will have a group whose interests line up with yours. Sports, politics, running, boating, biking, car fanatics, book clubs, gardening clubs, gambling groups, bowling leagues, ball teams, preppers, shooting clubs, community aid groups, you name it, Chicago has it. All you have to do is get out there and meet them. If you can't make friends in Chicago, then its time to move out west someplace far from others and live in a shack by yourself, because you are the king of introverts!
The hardest part about making friends in a place like Chicago is picking ones you want to keep, as they are harder to get rid of, than to get. Good luck.